DOM Window unload event, is it reliable?

Question

Can I rely on the window unload event to be triggered when a user closes a tab/window/browser?

Edit:

Found a list of what triggers the unload event in IE. ht

Answer 1

Not in all circumstances no. The browser could crash etc. keeping the event from firing. The user could also use add-ons like Grease Monkey to prevent the event from firing also.